Sorry

From rare gemstone to mass market material for future iPhones, iPads and more?

Apple has hugely ambitious plans for synthetic sapphire. But to make them real, and affordable, Apple singlehandedly has to change the mineral Corundum, an aluminum oxide that is better known as sapphire, from a rare gemstone into a mass market industrial material.

Long-prized as a gemstone, sapphire has been increasingly important – in synthetic form - as an industrial material. But its relatively high cost has stymied wider user of its optical clarity, incredible hardness, and dielectric properties. Apple has made sapphire a strategic investment: if successful, the company will drive sapphire into new, mass market uses, starting with its own mobile products.

Apple has been using small sapphire disks as covers, first for the iPhone 5 camera and most recently for the iPhone 5S Touch ID home button structure (shown here in exploded view, the sapphire cover at right). But the company is paying $578 million to equip an Arizona factory with sapphire furnaces that will produce an enormous amount of sapphire. The rumored reason: a sapphire cover for an iPhone display in 2014 or 2015.

The Mesa, Ariz., production site is equipped with the Advanced Sapphire Furnace (AFS, show here), from GT Advanced Technologies. These GTAT furnaces use a variation of what's known as the Czochralski melt-growth process: it combines melting with directional cooling to create a very large sapphire crystal of very high purity.

This schematic outlines how GTAT's AFS creates the raw sapphire. Sapphire is a variety of the mineral corundum (or aluminum oxide). The process starts with a seed sapphire crystal that has a specific crystalline orientation. The aluminum oxide growth mixture is added, and heated to its melting point of 2,040 degrees Centigrade. For the AFS, heat is then extracted from the bottom up until the growth is complete. The entire process takes about 15 days.

The end result is a hockey-puck shaped mass of colorless sapphire. In nature, iron and titanium impurities give sapphires a distinctive blue color, while chromium creates another corundum gem: ruby. The AFS can produce various sizes, the largest is about 15 inches high and 15 inches in diameter, weighing about 253 pounds. But that's only the beginning.

Apple will ship the boules to partners in Asia where the hockey pucks will be cut into blocks with diamond saws or wire, polished, shaped, and prepped for assembly into the final product, rumored to be a cover glass for a 2014 iPhone. Sapphire's hardness adds time and complexity to all of these steps, calling for significant supply chain investments. And, surprisingly, it can be prone to fracturing during this stage.

You can get a sense of what to expect from a sapphire-screen iPhone in this video, from Aero-Gear, which currently offers its adhesive-backed Flight Glass SX Sapphire Crystal protective screen for the iPhone 4, 5, and 5s, priced at $69. Rubbing a heavy cement block back and forth over the thin sapphire screen left a visible residue of grit and dust…but not one scratch.